Kate, 31, stunning in a Jenny Packham pale gold full-length sequin gown with crystal motif, accompanied husband William for the first Tusk Conservation Awards, part of his African charity.

"As you might have gathered, Catherine and I have recently become proud parents – of a baby who has a voice to match any lion's roar!" the proud dad, 31, said to applause, asking that guests pardon the couple's anxiety.

"This is actually our first evening out without him, so please excuse us if you see us nervously casting cheeky glances at our mobile phones to check all is well back home."

And Kate, who teamed her gown with Jimmy Choo sandals and a diamond bracelet said to have been a wedding gift
from her father-in-law, Prince Charles, told a well-wisher that 7½-week-old George "has a mix of both of us."

The couple said they'd left Prince George at home with his nanny Jessie Webb, 71, who's recently stepped in to help the young family. She also looked after Princes William and Harry when they were boys.

The evening reception came after the Palace confirmed William was leaving the armed forces to start new roles in public life.

The charity Tusk, which aims to secure a peaceful co-existence for Africa’s wildlife and its people, set up the awards to mark "outstanding achievement in the field of African conservation."

In his speech, William highlighted the theme of the inaugural award night. "Like any new parents, our thoughts inevitably turn to the world that our child will
inherit. It is unfathomable to imagine a world in which children who have been born in the past couple of months may grow up in a world in which rhinoceros have ceased to live in the wild."

And he pointed to the "scary" statistic that 35,000 elephants were killed for their ivory in the last year.

"The possibility of extinction is bad enough for one of our children growing up here in the West, who will never experience the magic of seeing a rhino on a new television documentary; or even for my own little George, who Catherine and I very much hope to introduce to east Africa
– a place we know and love – in the fullness of time.

"But for a child growing up in Africa and whose birth-right and economic inheritance these creatures are, it is nothing more than immoral that he or she may never experience what his parents and grandparents knew and treasured."